WASHINGTON — For more than a decade, Richard Matte has suffered through a series of grave illnesses. The 70-year-old from Chicopee has a transplanted heart. He’s been treated for bladder cancer, lung cancer, and nerve disorders.

But it wasn’t until 2011 that the retired master sergeant learned he and fellow veterans of the Air Force Reserve’s 731st Tactical Airlift Squadron in Westover might have been exposed to traces of Agent Orange. Matte quickly looked up ailments designated by the Department of Veterans Affairs as linked to contact with the deadly herbicide.

“I'm sitting here thinking, ‘Jeez, I got about 10 of these myself,’ ” Matte, who recently had his left leg amputated, recalled in an interview.

But unlike hundreds of thousands of other veterans who have been compensated by the VA for Agent Orange exposure during the Vietnam War, Matte never served in Southeast Asia or directly handled the deadly substance. The C-123 Provider cargo planes he crewed had been used to dump thousands of canisters of the toxin over Vietnam, before being brought home to Westover and used for domestic missions from 1972 to 1982.

It turns out those old planes were contaminated with toxic residue. Once they were retired for good, the Air Force even cordoned them off at a remote desert airstrip in Arizona and treated them as hazardous waste.

Despite growing evidence that the fliers were exposed to the poison, the VA is denying claims made by Matte and other veterans from the 731st Tactical Airlift Squadron, saying they are not eligible for special Agent Orange-related benefits mandated by Congress — health care as well as disability and survivor benefits.

SUZANNE KREITER/GLOBE STAFF

Richard Matte of Chicopee has a transplanted heart and has been treated for bladder cancer, lung cancer, and nerve disorders.

The VA is sticking to its long-held position that the exposure to Agent Orange by these veterans was “minimal.” It asserts that “it is unlikely that sufficient amounts of dried Agent Orange residue could have entered the body to have caused harm.”

Pleas for help from Matte and other veterans in his situation have garnered press coverage over the years. But pressure has been mounting on the VA as more public health agencies, toxicology experts, and private physicians weigh in on their behalf, asserting that their illnesses could be the result of exposure to Agent Orange.

The C-123 Veterans Association says it knows of up to 50 Massachusetts residents — or their survivors — who are in the same predicament as Matte.

The federal Centers for Disease Control and Prevention said last year, based on new analysis of swipes taken from several of the planes in the 1990s and shortly before they were disposed of in 2010, that the planes clearly contained a toxic residue, and crew members had a “200-fold cancer risk.”

In April, a team of medical researchers that included public health experts from New York and Boston concluded that “the potential for dioxin exposure to personnel working in the aircraft post-Vietnam is greater than previously believed and that inhalation, ingestion, and skin absorption were likely to have occurred during post-Vietnam use of the aircraft by aircrew and maintenance staff.”

US AIR FORCE

A C-123 Provider plane of the type used in Vietnam and later flown by Matte on domestic missions.

The findings, published in the journal Environmental Research and sponsored in part by the Air Force School of Aerospace Medicine, “contrast with Air Force and VA conclusions and policies,” wrote Jeanne Mager Stellman, professor emerita at the Mailman School of Public Health at Columbia University.

The reports have persuaded Representative Richard Neal, a Democrat from Springfield who represents many of the afflicted veterans, that the Pentagon and VA have to adopt a different approach to these claims.

“Taking into account this information and the high levels of illnesses known to be linked to Agent Orange occurring in these Westover veterans, I believe these men and women are entitled to the same benefits granted to those who served on the ground in Vietnam,” Neal wrote earlier this month to the Department of Veterans Affairs.

In a statement, a VA spokeswoman, Meagan Lutz, said the agency “wants to ensure that all veterans, including those who served on C-123s, receive the benefits to which they are entitled under the law. VA will continue to review new scientific information on this issue as it becomes available.”

But the Air Force’s own handling of the planes shows it believed the aircraft posed a health hazard.

Records released under the Freedom of Information Act in 2011 revealed the Air Force confirmed the planes were contaminated by “herbicide residue” in 1979, following complaints of maintenance personnel.

A sampling found residue of the dioxin in Agent Orange and concluded that “it may ultimately be necessary to completely deodorize the aircraft.”

One of the planes was tested a decade and a half later — in 1994 — before being placed in an Air Force museum in Ohio and was similarly found to be contaminated.

Beginning in 1998, the Air Force kept the planes in quarantine at an Arizona base and decided in 2009 not to sell the aircraft or parts, citing “Agent Orange contamination during the Vietnam War.”

That is yet another source of consternation to the C-123 veterans.

“My colleagues who flew the C-123 with me and worked on the C-123s are not afforded the benefit of VA recognition, notwithstanding the fact they are coming down with the same illnesses,” said retired Colonel Archer Battista, 68, of Belchertown, Mass., who piloted the C-123s at Westover for nearly 25 years and is trying to raise awareness about their plight.

Battista, himself a prostate cancer survivor, is one of the only C-123 veterans who are eligible for Agent Orange-related benefits — but that is because unlike most of the others he served on active-duty in Vietnam before he joined the reserve unit at Westover.

“For me it is really a moral quest,” said Battista, who is also a lawyer. “I think VA is wrong, dead wrong in the position it has taken.’’

“I know guys and gals I flew with — good friends — ought to be entitled to the same,’’ he said. “This is a fight for our friends and we think it is a very important one.”

The VA has designated as service-related more than a dozen diseases — including certain heart ailments, forms of diabetes, cancer, leukemia, Parkinson’s disease, as well as birth defects in their children — for those who were exposed to Agent Orange on the battlefield or handled it as part of their duties between 1962 and 1975.

According to the Congressional Research Service, some 600,000 veterans of the Vietnam era have participated in the VA’s so-called Agent Orange Registry that makes them eligible for an examination, a series of laboratory tests and, if approved, a range of benefits.

At least 10 Westover veterans have applied for Agent Orange benefits and have been denied, said retired Major Wes Carter of Andover, a former pilot who heads the C-123 Veterans Association.

The only exception was retired Lieutenant Colonel Paul Bailey of Bath, N.H., but his benefits were approved only at the 11th hour.

Sufffering from prostate cancer that he believed was due to dioxin exposure during his service in the 731st, he sought VA health benefits in 2011. After nearly two years he was informed he was being denied.

After his case received some media attention and congressional scrutiny, the VA changed its position, making him the only post-Vietnam C-123 veteran to be eligible for Agent Orange benefits.

“He died a few months later,” says his widow Nancy Bailey, 65. “It was too late. It would have been nice if they had not denied his claim when he first got sick.”

But because of the benefits he was ultimately approved for, she says, she is receiving a special survivor benefit in the form of $1,250 non-taxable income each month.

“I guess I shouldn’t complain because he is the only one who they have given the claim to,” she said. “But I am very concerned about all the other veterans. The VA is really fighting hard.”

Like other veterans and their families, she believes there was a “big coverup’’ about how contaminated the planes really were.

Many believe they never should have been operated at all following what was known as Operation Ranch Hand, the military operation between 1962 and 1971 that sprayed an estimated 20 million gallons of herbicide over Vietnam to deprive the communist Vietcong of food and vegetation cover.

Now the VA has commissioned its own independent study on their potential exposure. The study, underway at the National Academy of Sciences,
is slated to be completed in September. The veterans express deep frustration that they will have to wait longer for the VA to make a new determination.

“The rest of the federal government disagrees with VA and has concluded C-123 veterans were exposed,” said Carter. “How many more expert opinions will it take?”

Matte, for his part, says he has given up trying to seek compensation for Agent Orange exposure.

“They can bury you under a mountain of paperwork and it never seems to be enough.”